Cold setting sand for foundry moulds and cores

ABSTRACT

A cold setting sand for moulds and cores comprises a refractory filler and an acid, wherein the acid used is organic acid with the dissociation constant of 10 -5  to 10 1 , with the components being contained therein in the following amounts, in percent by weight: 
     
         ______________________________________                                    
 
    
     refractory filler    from 95 to 99                                        
organic acid         from 1 to 5.                                         
______________________________________

BACKGROUND OF THE INVENTION

The present invention relates to foundry practice and more in particular to a cold setting sand for foundry moulds and cores.

There is known a foundry sand which comprises a refractory filler containing magnesium and/or chromium oxides, such as chrome-magnesite or magnesite-chrome, and a binder such as alcohol-sulfite lye or water glass (A. M. Liass, "Fast Setting Foundry Sands", Mashinostroenie Publishers, Moscow, 1965).

There is also known a cold setting sand which comprises a filler, orthophosphoric acid and a powdered material containing iron oxides.

The prior art sands are disadvantageous in that they are difficult to shake out, have insufficient strength, and require heat drying. Furthermore, the powder material containing iron oxides requires pregrinding, which makes the production more complicated and expensive, and damages to cores during their removal from core-boxes and subsequent handling.

DISCLOSURE OF THE INVENTION

What is required to a cold setting sand for moulds and cores of such composition having high strength, and not requiring heat drying and pregrinding of the starting materials.

The invention provides a cold setting sand for foundry moulds and cores, comprising a refractory filler and an acid, wherein the acid used is an organic acid with a dissociation constant of 10⁻⁵ to 10¹, the components being contained therein in the following amounts, percent by weight:

    ______________________________________                                         refractory filler   from 95 to 99                                              organic acid        from 1 to 5                                                ______________________________________                                    

A decrease in the amount of organic acid below 1.0 percent by weight will make it impossible to prepare a sand of the required strength, whereas an increase of this amount above 5.0 percent by weight will have no substantial effect on the sand properties.

The foundry sand of the invention lends itself readily for the knocking-out operation, has high strength and rapid setting rates, and requires no heat drying.

The refractory filler used in the sand of the invention is preferably magnesium oxides, and/or chromium oxides, and/or iron oxides, and/or silicon oxides, and the organic acid with the dissociation constant of 10⁻⁵ to 10¹ is preferably an aromatic sulfonic acid or carboxylic acid.

Such selection of fillers and acids makes it possible to produce a cold setting sand of good technological properties.

Preferably, the cold setting sand of the invention additionally comprises orthophosphoric acid taken in a ratio to organic acid as 0.1:1 to 4:1.

The above organic acid/orthophosphoric and ratio of 1:0.1 to 1:4 permits the sand setting rates to be regulated in accordance with various production conditions. A lower content of orthophosphoric acid will have no effect on the technological properties of the sand, whereas a higher content will bring down the sand setting rate to an inadmissibly low level.

BEST MODE FOR CARRYING OUT THE INVENTION

According to the invention, the cold setting sand is prepared by stirring a mixture of the refractory filler and acid for 1-2 min.

The acid is preferably introduced undiluted, or in solution. In the latter case, the total amount of solution should be increased so that the content of acid as calculated for the undiluted acid will be within the range of 1 to 5.0 percent by weight.

The sand of the invention may be prepared both with the use as the filler of pure oxides of magnesium, and/or chrome, and/or iron, and/or silicon, or materials containing these oxides, for example, magnesite, chrome-magnesite, magnesite-chrome or a mixture thereof. The above-mentioned oxides or materials containing them can be also used in combination with other refractory fillers, such as quartz sand, zircon, kyanite-sillimanite, etc.

The aggregate content of the above-mentioned oxides in the refractory filler should be in the range of from 2.0 to 100 percent by weight.

Table 1 gives, as an example, the chemical composition of chrome-magnesite, magnesite-chrome and chrome ironstone, which are used as the refractory filler in the cold setting sand of the invention.

                                      TABLE 1                                      __________________________________________________________________________     Chemical composition, %                                                                                          The                                          Filler                                                                               MgO Cr.sub.2 O.sub.3                                                                   Al.sub.2 O.sub.3                                                                   FeO Fe.sub.2 O.sub.3                                                                   SiO.sub.2                                                                          CaO rest                                         __________________________________________________________________________     Magne-                                                                               62-71                                                                               9-17                                                                              3-7 --  4-7 3-7 3-6 0.3-                                         site-                             8.8                                          chrome                                                                         Chrome-                                                                              51-57                                                                              18-22                                                                              5-7 --   7-10                                                                              3-5 3-4 0.3-                                         magne-                            9.8                                          site                                                                           Chrome                                                                               14-18                                                                              52-58                                                                               8-10                                                                              11- --  2-5 --  0.9-                                         iron-             14              1.1                                          stone                                                                          __________________________________________________________________________

The rate of setting and strength of the sand may be regulated by altering the granulometric composition of oxides. Therefore, the sand composition should include such oxides in which the amount of fractions having less than 0.1 mm in size ranges from 5.0 to 100.0 percent by weight. The use of oxides with a lower amount of such fractions adversely affects the rate of setting and strength of the sand. An increase in the amount of small-size fractions (below 0.1 mm) results in higher setting rates and strength of the sand.

Table 2 gives the granulometric composition of the oxides used in the sand composition.

                                      TABLE 2                                      __________________________________________________________________________              Mesh size                                                                      2.5                                                                              1.6                                                                               1.0                                                                               0.63                                                                              0.4                                                                               0.315                                                                             0.2                                                                               0.16                                                                              0.1                                                                               0.063                                                                             0.05                                                                              0.05                                                                              Clay                               No.                                                                               Filler                                                                               Sieve residue, %                   component, %                       __________________________________________________________________________     1  Magnesite-                                                                           1.4                                                                              4.38                                                                              10.96                                                                             12.4                                                                              15.76                                                                             7.28                                                                              11.2                                                                              8.32                                                                              10.68                                                                             10.26                                                                             2.86                                                                              0.66                                                                              3.84                                  chrome                                                                      2  Chrome-                                                                              --                                                                               0.08                                                                              2.44                                                                              6.92                                                                              11.0                                                                              9.7                                                                               6.42                                                                              6.20                                                                              7.85                                                                              10.58                                                                             5.90                                                                              19.0                                                                              13.44                                 magnesite                                                                   3  Chrome                                                                               1.2                                                                              3.16                                                                              4.57                                                                              8.71                                                                              19.8                                                                              11.42                                                                             9.23                                                                              7.84                                                                              12.56                                                                             11.66                                                                             3.29                                                                              5.34                                                                              1.22                                  ironstone                                                                   __________________________________________________________________________

Standard samples were made from the sand by charging the latter into blocks and its subsequent compacting. The samples were then tested for compressive strength (in kg/cm²).

The knocking-out characteristic is determined by the residual strength of the sand at high temperatures, found after heating and cooling the sand samples.

The invention is further described by the following illustrative Examples.

EXAMPLE 1

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite        99                                                     Formic acid             1                                                      ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and formic acid for 1-2 min.

Standard samples were made from the resultant sand by charging the latter into blocks and its subsequent compacting.

The standard samples were tested for compressive strength which was 4.0 kg/cm² after 1 hour; 5.5 kg/cm² after 4 hours; and 8.0 kg/cm² after 24 hours.

EXAMPLE 2

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite        97                                                     Formic acid             3                                                      ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and formic acid for 1-2 min.

The standard samples from the sand were tested for compressive strength, which was 14.0 kg/cm² after 1 hour; 19 kg/cm² after 4 hours; and 23.5 after 24 hours.

EXAMPLE 3

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite        95                                                     Formic acid             5                                                      ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and formic acid for 1-2 min.

The standard samples from the resultant sand were tested for compressive strength, which was 16.5 kg/cm² after 1 hour; 21.0 kg/cm² after 4 hours; and 26.5 kg/cm² after 24 hours.

EXAMPLE 4

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Magnesite-chrome        97                                                     Formic acid             3                                                      ______________________________________                                    

The sand was prepared by stirring the mixture of refractory filler and formic acid for 1-2 min.

The standard samples from the sand were tested for compressive strength, which was 15.0 kg/cm² after 1 hour; 19.0 kg/cm² after 4 hours; and 23.5 kg/cm² after 24 hours.

EXAMPLE 5

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome ironstone         97                                                    Benzenesulfonic acid     3                                                     ______________________________________                                    

The sand was prepared by stirring the mixture of refractory filler and acid for 1-2 min.

The standard samples from the resultant sand were tested for compressive strength, which was 14.5 kg/cm² after 1; 17.0 kg/cm² after 4 hours; and 22.5 kg/cm² after 24 hours.

EXAMPLE 6

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite  48.5                                                         Magnesite chrome  48.5                                                         Maleic acid       3                                                            ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and acid for 1-2 min.

The standard samples from the resultant sand were tested for compressive strength, which was 15.5 kg/cm² after 1 hour; 20.0 kg/cm² after 4 hours; and 24.5 kg/cm² after 24 hours.

EXAMPLE 7

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Quartz sand             82                                                     Magnesium oxides        15                                                     Acetic acid             3                                                      ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler (a mixture of quartz sand and magnesium oxides) and acid for 1-2 min.

The standard samples made from the sand were tested for compressive strength, which was 14.5 kg/cm² after 1 hour; 17.0 kg/cm² after 4 hours; and 22.0 kg/cm² after 24 hours.

EXAMPLE 8

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite   97                                                          Maleic acid        1.5                                                         Orthophosphoric acid                                                                              1.5                                                         ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and acids for 1-2 min.

The standard samples made from the resultant sand were tested for compressive strength, which was 13.0 kg/cm² after 1 hour; 16.5 kg/cm² after 4 hours; and 22.0 kg/cm² after 24 hours.

EXAMPLE 9

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite   96.7                                                        Maleic acid        3.0                                                         Orthophosphoric acid                                                                              0.3                                                         ______________________________________                                    

The sand was prepared by stirring the mixture of the refractory filler and acids for 1-2 min.

The compressive strength of the standard samples made from the resultant sand was 15.0 kg/cm² after 1 hour; 18.0 kg/cm² after 4 hours; and 23.5 kg/cm² after 24 hours.

EXAMPLE 10

A sand was prepared from the following components, in percent by weight:

    ______________________________________                                         Chrome-magnesite   97                                                          Maleic acid        0.6                                                         Orthophosphoric acid                                                                              2.4                                                         ______________________________________                                    

The resultant mixture of the refractory filler and acids was stirring for 1-2 min.

The compressive strength of the standard samples made from the resultant sand was 6.5 kg/cm² after 1 hour; 11.0 kg/cm² after 4 hours; and 26.0 kg/cm² after 24 hours.

EXAMPLE 11 (COMPARATIVE)

Table 3 gives the residual compressive strength data for the prior-art sand (comprising 94 parts by weight of quartz sand used as a filler; 6 parts by weight of powdered ferrous oxide; and 6 parts by weight of orthophosphoric acid) and for the sand according to the present invention.

                  TABLE 3                                                          ______________________________________                                                   Compressive strength,                                                Temperature,                                                                             kg/cm.sup.2                                                          °C.                                                                               20    200    400  600  800  1000 1200 1400                           ______________________________________                                         Prior-art sand                                                                           13    5.6    5.0  4.5  2.0  1.1  11.6 13.0                           Sand according                                                                           18    2.4    1.6  1.0  0.6  0.4  0.4  5.2                            to the invention                                                               as illustrated                                                                 in Example 3                                                                   ______________________________________                                    

INDUSTRIAL APPLICABILITY

Cores and moulds from the cold setting sand of the invention may be used for the production of castings from steel, cast-iron and nonferrous alloys. 

We claim:
 1. A cold setting sand comprising:from 95 to 99 weight percent of a refractory filler containing magnesium oxides, iron oxides, silicon oxides or mixtures thereof and from 1 to 5 weight percent of an organic acid having a dissociation constant of 10⁻⁵ to 10¹.
 2. The sand of claim 1, also containing orthophosphoric acid in a ratio to said organic acid of 0.1:1 to 4:1.
 3. The sand of claim 1, wherein said aromatic acid is a carboxylic acid or a sulfonic acid.
 4. The sand of claim 1, wherein said filler contains from 2 to 100 percent by weight of said oxides.
 5. The sand of claim 1, wherein said filler consists of chrome-magnesite, magnesite chrome or chrome-ironstone.
 6. The sand of claim 1, wherein 5.0 to 100.0 percent by weight of said oxides have a particle size less than 0.1 mm.
 7. A sand according to claim 1 comprising 95 to 99 percent by weight of chrome magnesite and 1 to 5 percent by weight of formic acid.
 8. A sand according to claim 1 comprising 97 percent by weight of chrome-ironstone and 3 percent by weight of benzenesulfonic acid.
 9. A sand according to claim 1 comprising 48.5 percent by weight each of chrome-magnesite and magnesite chrome and 3 percent by weight of maleic acid.
 10. A sand according to claim 1, comprising 82 percent by weight of quartz sand, 15 percent by weight of magnesium oxides and 3 percent by weight of acetic acid.
 11. A sand according to claim 1 comprising in weight percent:

    ______________________________________                                         Chrome-magnesite        97,                                                    Maleic acid             1.5 and                                                Orthophosphoric acid    1.5.                                                   ______________________________________                                    


12. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite        96.7,                                                  Maleic acid             3.0 and                                                Orthophosphoric acid    0.3.                                                   ______________________________________                                    


13. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite       99 and                                                  Formic acid           
 1.                                                      ______________________________________                                    


14. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite       97 and                                                  Formic acid           
 3.                                                      ______________________________________                                    


15. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite       95 and                                                  Formic acid           
 5.                                                      ______________________________________                                    


16. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Quartz sand            82,                                                     Magnesium Oxides       15 and                                                  Acetic acid           
 3.                                                      ______________________________________                                    


17. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite       48.5,                                                   Magnesite chrome       48.5 and                                                Maleic acid           
 3.                                                      ______________________________________                                    


18. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome ironstone        97 and                                                 Benzenesulfonic acid   
 3.                                                     ______________________________________                                    


19. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Magnesite-chrome       97 and                                                  Formic acid           
 3.                                                      ______________________________________                                    


20. A sand according to claim 1, comprising in weight percent:

    ______________________________________                                         Chrome-magnesite        97,                                                    Maleic acid             0.6 and                                                Orthophosphoric acid    2.4.                                                   ______________________________________                                     